Method of eliminating gas pockets in liquid filled cables



April 26, 1938. v o. GASSER 2,115,574

METHOD OF ELIMINATING GAS POCKETS IN LIQUID FILLED CABLES Filed Sept. 7, 1954 Vaeuum pump Inventor: Otto Gas ser- Hi Attorney.

' Patented Apr. 26,1938

. 2,115,574 a I METHOD or ELIMINATING GAS rocxn'rs.

IN LIQUID FILLED CABLES Otto Berlin-('iharlottenburg, Germany, assignor to Siemens Schuckertwerke Aktiengesellscli'ait, a corporation of Germany I Application September '1, 1934; Serial No. 743,163

' .lnGerrna-ny September 14, 1933 ,6 Claims. (o1. 173-264),

is known, the presence or pockets anywhere within the sheath of a high potential cable containing air -or other gas constitutes a potential,

source of danger because of the ionization of the j gas in the pockets which is bound to take place.

This ionization phenomenon gradually brings about the destruction of the insulation by burning.

To reduce ionization troubles in a cable due to.

gas pockets during operation thereof, it is the practice to impregnate the insulation on theconductor with a thin liquid, such as oil, and to connectvariable capacity reservoirs to the channel of.the cable at spaced intervals into and from which the liquid is free to flow as its temperature changes. found largely to eliminate the presence of gas pockets, it does not do so as completely as is desired.

2 My invention has for its object to improve the constructionof electric cables by eliminating gas pockets therefrom as completely as possible, and

' especially Irom within the body of insulation on 1 the conductor.

In the. accompanying drawing is diagrammatically illustrated suitable my invention. r As ordinarily constructed, a cable comprises one or more conductors each of'which is'stranded to increase its flexibility, and over the bundle of strands is a body of insulation in the form of wrapped on tape composed of fibrous material, such as paper for example. In such a cable,'there is a tendency for gas pockets to be formed in-the body of insulation itself, as for example between the layers or turns and also between; the edges of the turns. in the strand spaces of the'conductor'.

the cable into service, the interior of the sheath and its contents is subjected to a liquid 'under a very strong pressure so as to cause it to fully penetrate all parts thereof. To distinguish this liquid from the final impregnating oil orcompound, it is referred to as a scavenging liquid.

After the scavenging liquid is removed, degasi- 55 and other gases which were contained in the ca- While such an arrangement has been.

means for carrying out Such pockets also tend' to form In carrying out my invention, prior to putting ble. The liquid not only removes gas irom' the channel but from 'the' strandspaces and the body of insulation as well. In the case of amulticonductor cable, it also removes gas from the filler spaces and from the insulation therein contained.

The pressure may be maintained on the scavenging liquid within the sheath by apump or other means, the liquid enteringthe cable at one end, the-other-end of the cable' being closed. Subseq'uently, the supply of liquid to the cable is cut ofi and the end which was initially closed is con-'- nected to or is opened into a suction device such as a vacuum tank or pump which removes the scavenging liquid. This alternate application of pressure and release thereof has the effect of causing impulses or. pulsations within the cable which causes the air and other gas inthe cable to move to the outside thereof as-distlnguished from being'pocketed therein or accumulating in.

some region thereof. "I'he'action of alternately -admitting'and removing scavenging liquid may and generally should be repeated so as to'ensure removal of the contained gases from the cable to a high degree.

The scavenging liquid after it is renioved. from the cable by the suction means may at thesame time or subsequently be relieved of the gases which 'it-has picked up, or absorbed in passage throughthe cable, thus permitting its further use. This may be done by any suitable means.

to obtain the impulse or pulsating eflect to start the gases intoxmotion with the moving stream, the liquid may be subjected to a series of drops inpressure in the courseof each scavenging operation-by manipulating a throttling means'arranged between the source of supply and-the cable or at the outlet or. region of discharge of said liquid.

has been found that a much better removal of air and the elimination of air pocketsfroin the cable length is obtained than by simply cleaning itwithagas. Y

In the drawing, l indicates a cable length or section of cable of usual construction from which gas is to be removed. The-length or section is closedat its ends by insulated terminals or end bells 2, or the endsmay be-clo'sed by other suit-- connected pipes 3 and 4, theformer supplying scavenging oil to the cable length and the latter" receivingthe 'oil and entrained airdischarged 30 Instead of alternately applying pressure to the liquid and then releasing such pressure in order 4.:- By utilizing .the method herein set iorth, it 1 therefrom. In the pipes are valves I and 6 by means of which the fiow of scavenging oil through the pipes and cable length may be shut off or the flow decreased, as desired. 1 indicates a pressure pump which receives oil from the tank 8 and delivers it to the cable length I. The pipe 4 discharges oil into the sealed tank! to which is connected a vacuum pump and degasifying means I0. II and I2 indicate gauges by means of which the pressure conditions in the pipes may be ascertained;

The operation is as follows: Initially scavenging oil is pumped witha steady flow from the pump '1 through the cable length into the tank 9 which has the efiect of removing a large part of the gas contained in the cable. As soon as the condition of the oil leaving the cable length indicates that gas is no longer being entrained, the

oil pressure within the cable length is changed. This can be done, for example, by closing valve B and leaving valve 5 open, the pressure pump 1 meanwhile continuing to operate and thus increase the pressure in the cable len th. If valve 6 is then suddenly opened, the discharged oil, i. e.,

' while the operation of the vacuum pump 1 or nately subjecting the liquid to changes of pres-- opening the valve 6 results in a decrease of pressure in the cable and drainage of oil therefrom. During the subsequent washing of the cable length, it will again be possible to removega certain quantity of gas from the cable, the quantity becoming less with each washing. These pressure changes, in conjunction with the subsequent flow of oil through the cable length, are repeated until the desired degree of removal of gas from the cable length is attained. The pressure changes outlined'above need not necessarily be effected in the precise manner mentioned above since the arrangement shown permits of considerable variation in this particular. While the scavenging oil need not necessarily be degasified in the earlier steps in the process, it is desirable before the final filling of the cable to pass well degasified oil through the cable length in order to'prevent the danger of a" new gas separation and also to absorb any small quantities of gas which may still be present in the cable length.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. Method of removing gas from the interior of a cable having a conductor, impregnated insulation thereon, and an impervious sheath, while it is not in service, which comprises subjecting the interior of the sheath to a scavenging liquid having initially a low gas content, alteron the liquid, and finally evacuating the cable and removing the liquid and its absorbed gases.

3. The method of removing gas from the interior of a cable having a conductor, impregnated insulation thereon and an impervious sheath, which comprises scavenging the interior. of the cable by subjecting it to a liquid under relatively high pressure which has initially a low gas content, reducing the pressure of the liquid, then removing it together with its absorbed gases, again filling the cable with scavenging liquid having a low gas content, and finally evacuating the cable to remove the liquid and its entrained gases.

4. The method of preparing for service an electric cablehaving a conductor, impregnated insulation thereon containing gas and an impervious sheath, which comprises subjecting the interior of the sheath to a scavenging liquid having initially a, low gascontent, alternately subjecting the liquid to pressure and release thereof, causing the scavenging liquid with its contained gas to be drained from the cable, and subsequently filling the cable with the final degasified impregnating liquid.

5. The method of removing contained gases from an electric cable having a conductor, im-

' pregnated insulation therefor and an impervious sheath enclosing the conductor and insulation preparatory to putting the cable into service, which comprises the steps of supplying to the interior of the sheath so as to act on the materials contained therein a scavenging liquid under pressure, releasing the pressure, then draining the liquid from the sheath, repeating the aforesaid steps until the desired reduction of gas content is obtained, and subsequent to the final drainage step supplying the interior of the sheath with degasified impregnating liquid.

6. The method of treating a cable of the type having a conductor, impregnated insulation and impervious sheathing means to remove foreign matter, which comprises subjecting the contents of the sheath to a scavenging liquid under pres sure, alternately subjecting the'said liquid to changes of pressure, causing the liquid to be drained from the sheath together with the foreign matter entrained therewith, refilling the cable 

